Typically, coated glass articles are produced by continuously coating a glass substrate while it is being manufactured in a process known in the art as the “float glass process.” This process involves casting glass onto a molten tin bath which is suitably enclosed, then transferring the glass, after it has sufficiently cooled, to lift out rolls aligned with the bath, and finally cooling the glass as it is advanced across the rolls initially through a lehr and thereafter while exposed to the ambient atmosphere. A non-oxidizing atmosphere is maintained in the float portion of the process, while the glass is in contact with the molten tin bath, to prevent oxidation. An air atmosphere is maintained in the lehr. The chemical vapor deposition of various coatings may be conveniently performed in the bath or the lehr, or even in the transition zone therebetween.
The physical form of the reactants employed in glass coating processes is generally a gas, liquid, solid, vaporized liquid or solid, liquid or solid dispersed in a barrier gas mixture, or vaporized liquid or solid dispersed in a barrier gas mixture. The chemical vapor deposition process generally employs a vaporized liquid or solid, which is typically dispersed in a barrier gas mixture.
Chemical vapor deposition processes are well known in the art of coating glass substrates. For example, U.S. Pat. No. 5,090,985 discloses a method of preparing vaporized reactants by injecting a liquid coating precursor into a vaporization chamber and heating the precursor until it turns into a vapor. Simultaneously, a blend gas is admitted into the chamber and thoroughly mixed with the vapor. A set of mixing blades, in direct mechanical engagement with a motor, rotate inside the vaporization chamber and distribute the liquid precursor as a uniform, thin film onto the vaporization chamber walls. The vaporized precursor and blend gas mix and become a stream of vaporized reactants for pyrolytic decomposition at the surface of a hot substrate.
Typically, one or more seals are located between the motor and the vaporization chamber to prevent precursor vapor from reaching the motor. For example, at least one seal is typically located around the shaft connecting the mixing blades with the motor. The seals are designed to exude small amounts of oil. The oil, however, may mix with the precursor thereby contaminating the precursor. Also, the seals may fail due to dirt particles becoming located between the seal and the shaft. The particles cause the shaft and the seal to vibrate and the vibrations eventually cause the seal to weaken and fail. If a seal fails, large amounts of oil may leak into the vaporization chamber and/or precursor vapor may leak into the seal oil.
Magnetically driven motors are well known in the art for rotating an object without a direct mechanical connection between the motor and the object. Typically, the absence of a direct mechanical connection eliminates the need for drive shafts and seals around those shafts. For example, U.S. Pat. Nos. 4,790,911 and 4,913,777 disclose the use of a magnetically driven motor to rotate a container without a direct mechanical connection between the motor and the container.
U.S. Pat. No. 4,913,777 teaches a container having a closure with a driven magnet affixed thereto. A driving magnet is located outside the closure. Upon engagement of the driving magnet with the driven magnet, the closure is rotated thereby distributing solvent about the inside surface of the closure. The walls of the closure are heated resulting in the formation of a vapor of the solvent.
The rotation of the closure cannot, however, distribute a uniform, thin layer of precursor material on the entire inside surface of the closure. Additionally, the container of the '777 patent does not allow for the continuous and uniform addition of precursor and other gases into the closure typically required for chemical vapor deposition preparations.
It must be noted that the prior art referred to hereinabove has been collected and examined only in light of the present invention as a guide. It is not to be inferred that such diverse art would otherwise be assembled absent the motivation provided by the present invention.
Therefore, it would be desirable to have a magnetically driven means for mixing and consistently distributing the precursor material on the inside of the vaporization chamber. It would also be desirable to create a barrier between the corrosive vaporized reactants in the vaporization chamber and other components of the apparatus with a barrier gas.